lightning_distance in extended schema, units?

[Pat]

I'm working on migrating over to the extended schema and have a question on the lightning_distance column. My sensor outputs as km, but should I save this observation as miles in the database if my usUnits are 1?

Just looking for confirmation since I didn't see anything in the docs. 

[Tom Keffer]

Just make sure its units are consistent with whatever packet or record you put it in. The engine will take care of the rest. 

Details depend on whether you are adding lightning_distance to an existing packet, or if you are creating a packet.

-tk

On Thu, Jul 2, 2020 at 5:42 AM Pat <p...@obrienphoto.net> wrote:

I'm working on migrating over to the extended schema and have a question on the lightning_distance column. My sensor outputs as km, but should I save this observation as miles in the database if my usUnits are 1?

Just looking for confirmation since I didn't see anything in the docs. 

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[Pat]

Thanks. Currently I'm just putting it into the loop as the raw data which is in km. Sounds like I need to convert it to miles so it's consistent.

On Thursday, July 2, 2020 at 8:49:12 AM UTC-4, Tom Keffer wrote:

Just make sure its units are consistent with whatever packet or record you put it in. The engine will take care of the rest. 

Details depend on whether you are adding lightning_distance to an existing packet, or if you are creating a packet.

-tk

On Thu, Jul 2, 2020 at 5:42 AM Pat <p...@obrienphoto.net> wrote:

I'm working on migrating over to the extended schema and have a question on the lightning_distance column. My sensor outputs as km, but should I save this observation as miles in the database if my usUnits are 1?

Just looking for confirmation since I didn't see anything in the docs. 

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[Tom Keffer]

Then you need to check the unit system of the incoming packet (don't assume it's in US), then change lightning_distance into the appropriate unit for that unit system.

The goal is for the units within a packet to be in a consistent unit system. Doesn't matter what that unit system is --- just that all types within the packet are in that system.

-tk

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[Pat]

Got it, running weewxd, I see the usUnits: 1, so I assume I have a mismatch with this particular field?

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[Tom Keffer]

usUnits == 1 means that the packet uses the US Customary unit system. So, yes, you would have to change to miles. But, good extensions assume nothing. The function weewx.units.convertStd is a convenient way to ensure the correct units. For example, if "val" holds the distance in km, something like this would work (NOT TESTED):

record['lightning_distance'] = weewx.units.convertStd( (val, 'km', 'group_distance'), record['usUnits'])

-tk

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[Pat]

Excellent! Now to update the extension and convert all my archive records to miles instead of km. Always learning. Thanks again! 

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[Tom Keffer]

Again, I wouldn't "convert to miles." Instead, convert to whatever unit system the record is using. Let WeeWX take care of the rest.

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[Pat]

Yep, that's my plan for future records. 

For past records in the archive table, I need to convert those since they're in the wrong unit because I was not letting weewx handle the conversion previously. 

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